Venting and asking if he should have to commit?

Me and my SO have been together going on 6 years in September. I have 2 kids a 7 year old boy by another and a 3 year old girl she is his first and only. He lives with me and my kids Monday through Friday because of work and rents a house with a roommate which I feel is stupid because he only lives there maybe 8 days a month but pays half of the rent. He is off on the weekends but sometimes he goes to the other house without me and our kids. I feel that it is not right for him to do that because we don't see him since he works 1030 am to 10 pm. So besides venting I was wondering if it was wrong of me to ask for him to commit to me and our family and give up the other house. I want to get married and get a place together but he keeps saying we can't till we are financially stable I feel that is just a cop out but afraid to keep pushing the subject. Any advice welcome!